The present invention relates to a semiconductor device and a method for manufacturing the same and more particularly to a semiconductor device having a trench and a method for manufacturing the same.
A device isolation (deep trench isolation, or DTI) structure in which insulating film is filled in a trench with a high aspect ratio is disclosed in Japanese Unexamined Patent Publication No. 2002-118256.
In the technique described therein, a trench is first made in a surface of a semiconductor substrate and then a first insulating film is formed over the surface of the semiconductor substrate in a manner to fill the trench. An opening which reaches the first insulating film is made by anisotropic etching of the first insulating film, where the upper end corner of the opening of the first insulating film has a more gradual inclination than the upper end corner of the trench. The above anisotropic etching process also reduces the thickness of the first insulating film lying over the semiconductor substrate surface. After that, a second insulating film is formed over the semiconductor substrate surface in a manner to fill the opening.
After a DTI structure was formed as mentioned above, an electronic device such as a MOSFET (metal oxide semiconductor field effect transistor) is formed on the semiconductor substrate.